1. Technical Field
The present invention relates to a projection optical apparatus and a projector.
2. Related Art
There is a known projector of related art in which a light modulator modulates light emitted from a light source (emitted light) in accordance with image information and a projection optical apparatus enlarges and projects the modulated light. Some projectors project a wide-field-angle image on a screen or any other projection surface over a short distance. In such a projector, a short-focal-length projection optical apparatus is used as a projection optical apparatus capable of wide-field-angle projection over a short distance. In recent years, a projection system for achieving a wide filed angle over a short distance is formed not only of a refractive system but also of a refractive/reflective compound system.
JP-A-2011-85922 discloses an optical system using a fixed lens section, a movable lens section, and a concave mirror, specifically, a projection/image formation system having a configuration in which an oblique light flux in oblique projection is configured to be inclined to the optical axis by a small angle for effective avoidance of a situation in which a lens barrel truncates an image forming light flux.
Since a projection system for wide-filed-angle projection over a short distance (short-distance projection) has a very short distance from a projection optical apparatus to a screen, variation in aberrations resulting from focusing is greater than the variation in a typical projection optical apparatus. Further, such a projection system has a configuration in which a plurality of spherical lenses that are highly sensitive and aspherical lenses are used, and variance in the position where each of the lenses is disposed greatly affects the variation in aberrations. As a result, an image projected on the screen tends to suffer from field curvature, a decrease in contrast due to the variation in aberrations, and other disadvantageous effects, undesirably resulting in a large decrease in image quality. It is therefore necessary in the assembly of lens groups to minimize variance in the position where each of the lenses is disposed, perform post-assembly optical adjustment, and take other measures.
In a projection optical apparatus using a refractive system and a reflective system, to adjust the position of a lens after the assembly, for example, an image is projected via a reflection mirror, and the position of a lens in the refractive system is adjusted while the projected image is viewed in some cases.
In this case, as a method for the adjustment, it is conceivable to use a master projection optical apparatus (in this stage, an apparatus that includes a reflection mirror but includes no projection optical unit that forms the refractive system and is used only as a reference) and place a target projection optical unit under positional adjustment in the master projection optical apparatus to perform the positional adjustment. In this case, after the adjustment, it is necessary to remove the target projection optical unit from the master projection optical apparatus and reassemble the removed projection optical unit into a projection optical apparatus to be actually used (in this stage, an apparatus that includes a reflection mirror but excludes only the projection optical unit that forms a refractive system). However, since the master projection optical apparatus and the actual projection optical apparatus are different apparatus, and variance in assembly may undesirably produce aberrations when the target projection optical unit is reassembled into an actual projection optical apparatus even if an aberration-free state has been achieved by using the master projection optical apparatus.
In contrast, as another method for the adjustment, it is conceivable to use no master projection optical apparatus but incorporate a target projection optical unit under positional adjustment into a projection optical apparatus to be actually used as a product and adjust the position of the projection optical unit incorporated in the projection optical apparatus. In this case, the target projection optical unit after the adjustment is not required to be removed, whereby an aberration-free state obtained by the adjustment can be retained.
To actually perform the positional adjustment, the position of a target projection optical unit inside a projection optical apparatus is adjusted by using an adjustment tool from the outside of the projection optical apparatus in both adjustment methods described above. In this case, when no master projection optical apparatus is used, reflected projection light is blocked in some cases not only by the adjustment tool but also a lens that forms the refractive system, a holding frame that holds a lens, and other components. When a master projection optical apparatus is used, projection light is reflected at an adjusted angle of reflection and the reflected projection light is therefore not blocked.
Further, a projection optical apparatus configured, assuming that the positional adjustment is performed by using a projection optical apparatus to be actually used, in such a way that an adjustment tool or any other component does not block projection light causes problems, such as difficulty in performing short-distance projection and an increase in the size of the projection optical apparatus.
It is therefore desired, in a case where a reflective system is used, to provide a projection optical apparatus that allows adjustment of the position of a lens without reflected light blocked and a projector including the projection optical apparatus.